Method of fabricating storage capacitor in semiconductor memory device, and storage capacitor structure

ABSTRACT

A storage capacitor has a double cylinder type structure, with a small cylinder in a lower part thereof and a cylindrical lower electrode structure disposed on the cylindrical contact plug. A method of fabricating the storage capacitor includes: forming a contact hole for exposing an activation region of a transistor; depositing a conductive film to form within the contact hole a contact plug of the storage capacitor having a void therein; opening an upper part of the void of the contact plug; and covering a surface of the device with material to form the storage capacitor electrode, to obtain the storage capacitor electrode having a double cylindrical structure.

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. §119 from KoreanPatent Application 2002-41118, filed on Jul. 15, 2002, the contents ofwhich are hereby incorporated by reference in their entirety as if fullyset forth herein.

BACKGROUND AND SUMMARY

[0002] 1. Technical Field

[0003] The present invention relates to a fabrication of a semiconductordevice, and more particularly, to a method of fabricating a storagecapacitor of a semiconductor memory device, and a structure thereof.

[0004] 2. Description

[0005] In general, a semiconductor memory device, e.g., a DRAM, has atendency of a rapid reduction in an area of a unit cell, according to anincrease in density. A sufficient capacity of the capacitor constitutinga memory cell is required so as not to impair an operatingcharacteristic of the memory device. For example, a high-density deviceover 64 Mb typically uses a capacitor structure of a cylinder type. Incomparison with a fin or trench structure, etc., as a conventionaltechnique, such a cylinder type capacitor structure has a relativelylarge electrostatic capacity and also has an advantage in the aspect ofleakage current.

[0006] A widely known method of fabricating the capacitor having thecylinder structure, in general, includes the procedure of fabricating astorage capacitor as a lower electrode by using, as a mask, photoresistas a photosensitive film and an oxide film spacer.

[0007] FIGS. 1 to 4 are sectional views showing a fabrication of acylinder type storage capacitor according to such a technique. Thesectional structures shown in FIGS. 2 to 4 are progressed in sequence,to thus result in the device shown in FIG. 1.

[0008] Referring first to FIG. 2, a transistor constructed of a deviceisolation film 4, a gate electrode 6, a spacer 8 and source/drain 10 isformed through a general fabrication process on a semiconductorsubstrate 2. Then, a bit line 14 connected to the transistor is formedthrough a contact plug 12. Herewith, the gate electrode 6 and the bitline 14 are electrically isolated through a dielectric film, e.g., atetra-ethyl-ortho-silicate (TEOS) film, and the bit line 14 is coupledwith the source/drain region 10 a of the transistor through the contactplug 12. Thereon, a dielectric film 16, e.g., O₃-TEOS film is depositedentirely, and on an upper part thereof, a silicon nitride 18 isdeposited. Subsequently, photoresist is placed on an upper part of thesilicon nitride layer 18 and then a photolithography process is executedto thus form a photoresist pattern 20 for exposing the source/drainregion 10 b of the transistor. Through a use of this pattern as an etchmask, the silicon nitride 18 and the dielectric film 16 areanisotropically etched in sequence, to thus form a contact hole forexposing the source/drain region 10 b of the transistor, as shown inFIG. 2.

[0009] With reference to FIG. 3, the photoresist pattern 20 shown inFIG. 2 is removed, and then a storage electrode conductive film thatwill be formed as a storage capacitor, e.g., a polysilicon film 22 dopedwith impurities is deposited with a predetermined thickness. Then, on anupper part of this polysilicon film 22, a photoresist pattern 24 fordefining a region where a storage capacitor electrode will be formed, isformed. Thereon, a low-temperature oxide film is entirely deposited andthen is etched-back, to thus form a spacer 26 in a side wall of thephotoresist pattern 24. Through a use of the spacer 26 as the etch mask,the polysilicon film 22 is anisotropically etched by constant thickness,to produce the structure shown in FIG. 3.

[0010] Referring to FIG. 4, the photoresist pattern 24 is removed, andthen the polysilicon film 22 is etched by using the spacer 26 as theetch mask, to thus form a storage capacitor electrode 22 a of a cylindertype. Next, the spacer 26 is eliminated, and a dielectric film 28 isformed on an overall upper surface of the storage capacitor electrode ofthe cylinder type. Subsequently, a polysilicon film doped withimpurities is entirely deposited, and is patterned, to thus form a platecapacitor electrode 30 on an upper part of the dielectric film 28, thuscompleting the structure, as shown in FIG. 1.

[0011] The method of fabricating such a conventional cylinder typecapacitor has a limitation to largely use the electrostatic capacity ofthe storage capacitor that becomes a lower electrode.

[0012] That is to say, a tendency to higher density devices causes manyrestrictions in obtaining a larger sectional area between a storagecapacitor electrode and a plate electrode. Especially, if a height of acontact plug for connecting the storage capacitor electrode with asource or drain region of the transistor is high, an electrostaticcapacity can be reduced due to an increase of contact resistance.

[0013] Therefore, an object of the present invention is to provide amethod of fabricating a storage capacitor in a semiconductor memorydevice and a storage capacitor structure, to address the conventionalproblems.

[0014] Another object of the present invention is to provide a method offabricating a storage capacitor in a semiconductor memory device and astorage capacitor structure to be advantageously applied to ahigh-density device.

[0015] Still another object of the present invention is to provide amethod of fabricating a storage capacitor in a semiconductor memorydevice and a storage capacitor structure so as to obtain a largerelectrostatic capacity within a restricted area.

[0016] In accordance with one aspect of the present invention to achievethese objects, the method of fabricating a storage capacitor of asemiconductor memory device comprises the steps of: depositing a firstdielectric film and a second dielectric film on a substrate in an areawhere a memory cell transistor has been formed, and forming a definedfirst photoresist pattern on an upper part of the second dielectricfilm; anisotropically etching the second and first dielectric films byusing the first photoresist pattern as an etch mask, to form a firstcontact hole for exposing an activation region of the transistor;removing the first photoresist pattern, wet-etching the substrate withan etching solution having a difference in an etch ratio between thefirst and second dielectric films to form a second contact hole having anegative slope; depositing a conductive film to form within the secondcontact hole a contact plug of the storage capacitor having a voidtherein; performing an etchback to open an upper part of the void of thecontact plug; covering a structure produced by the preceding steps witha third dielectric film, and then forming a second photoresist patternfor defining a region where a storage capacitor electrode is to beformed; dry-etching the third dielectric film exposed through the secondphotoresist pattern; and removing the second photoresist pattern, andcovering a surface of the device with material to form the storagecapacitor electrode, to obtain the storage capacitor electrode having adouble cylindrical structure.

[0017] Herein, the first dielectric film is an oxide film, and thesecond dielectric film may be a nitride film, and the etching solutionpreferably is hydrofluoric acid (HF). The conductive film that willbecome the contact plug can be a doped polysilicon film.

[0018] To fabricate a plurality of memory cells, preferably, includedare the steps of covering the surface with an oxide film after producingthe storage capacitor electrode, and performing an etchback and a wetetching, to thus obtain the storage capacitor electrode divided into aunit of memory cell.

[0019] In accordance with another aspect of the present invention, thestorage capacitor of a semiconductor memory device has a structure of adouble cylinder that is extended by a constant depth from an upper partof a contact plug to a lower part thereof.

[0020] In accordance with yet another aspect of the invention, Acapacitor for a semiconductor device comprises: a cylindrical contactplug disposed within a first dielectric film formed on a substrate, thecylindrical contact plug having a first inner diameter and a first outerdiameter; a cylindrical lower electrode structure disposed on thecylindrical contact plug, the cylindrical lower electrode structurehaving a second inner diameter and a second outer diameter, where thesecond inner diameter is greater than the first inner diameter and thesecond outer diameter is greater than the first outer diameter; a seconddielectric film covering an interior surface of the cylindrical contactplug and both interior and exterior surfaces the cylindrical lowerelectrode structure; and an upper electrode formed on the seconddielectric film.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and other objects and features of the present inventionwill become apparent from the following description of preferredembodiments taken in conjunction with the accompanying drawings, inwhich:

[0022] FIGS. 1 to 4 are sectional views showing a fabrication of acylinder type storage capacitor; and

[0023] FIGS. 5 to 13 are sectional views showing in sequence afabrication of a cylinder type storage capacitor having adouble-cylinder type structure.

DETAILED DESCRIPTION

[0024] Hereinafter, a method of fabricating a storage capacitor in asemiconductor memory device and a storage capacitor structure accordingto preferred embodiments of the present invention will be described indetail with reference to FIGS. 5 through 13.

[0025] Constructive elements having the same or similar functions willbe described with the same or similar referential numbers even thoughrepresented on different drawings.

[0026] FIGS. 5 to 13 are sectional views showing in sequence afabrication of a cylinder type storage capacitor in accordance with anexemplary embodiment of the present invention.

[0027] Referring first to FIG. 5, a memory cell transistor constructedof a device separation film 4, a gate electrode 6, a spacer 8 andsource/drain regions 10, 11 on a semiconductor substrate 2 is formedthrough a general fabrication process. Then, a bit line 14 connected tothe memory cell transistor is formed through a contact plug 12.

[0028] Subsequently, a dielectric film 16, e.g.,boro-phospho-silicate-glass (BPSG), TEOS or a high-density oxide film,is deposited on the entire surface and thereon, a silicon nitride 18 isdeposited. Next, on an upper part of the silicon nitride 18, photoresistis covered, and then a photoresist pattern 20 for exposing the sourceregion 10 of the transistor through a photolithography process isformed. Through a use of this pattern as an etch mask, the siliconnitride 18 and the dielectric film 16 are anisotropically etched insequence through a dry etch, to thus form a contact hole 40 for exposingthe source region 10 of the transistor as shown in FIG. 5.

[0029] With reference to FIG. 6, the photoresist pattern 20 shown inFIG. 5 is removed by ashing, and then an etching solution, e.g., HF, isused to perform a wet etching, to thus form, in one body, contact holes41, 50 having negative slopes that are provided by a difference of etchratios between the silicon nitride film 18 and the dielectric film 16.

[0030] Next, with reference to FIG. 6, a conductive film of which acontact plug of the storage capacitor will be formed, e.g., polysilicondoped with impurities, is deposited on the entire surface with apredetermined thickness.

[0031] Then, as shown in FIG. 7, a void 60 is formed with a “negativeslope” in the interior of the contact hole. Advantageously, the void 60is usefully utilized for an increase of electrostatic capacity.

[0032] Subsequently to the stage shown in FIG. 7, an etchback isperformed entirely, to thus obtain a result as shown in FIG. 8. In FIG.8, an upper part of the void 60 is opened, to thus form a contact plug51 of a spacer type in the interior of the contact hole.

[0033] Following the stage shown in FIG. 8, an oxide film, e.g., a TEOSfilm 70 covers an entire surface, and a photoresist pattern 80 fordefining a region where a storage capacitor electrode will be formed, isformed to thus result in the structure shown in FIG. 9.

[0034] Subsequent to the stage shown in FIG. 9, a plasma dry etchingprocess is performed, to thus etch the TEOS film 70 exposed by thephotoresist pattern 80 and to result in the structure shown in FIG. 10.

[0035] In FIG. 10, the photoresist pattern 80 is removed by ashing, andmaterial for the lower capacitor electrode, e.g., a doped polysiliconfilm 110, is formed, to thus result in the structure of FIG. 11.

[0036] Referring to FIG. 11, beneficially the polysilicon film 110covers the interior of the contact plug 51 whose upper part is opened,to thus form a double cylinder type structure, with a small cylinder ina lower part thereof and a cylindrical lower electrode structuredisposed on the cylindrical contact plug. Such a structure for a lowercapacitor electrode provides a greatly increased electrostatic capacity.Beneficially, a surface of the lower capacitor electrode formed therebycan be processed with hemispherical silicon grains (HSG) to increase thecapacitance.

[0037] With reference to FIG. 12, an oxide film, e.g., an undopedsilicon glass (USG) film 115, covers the structure shown in FIG. 11.Next, an etchback and a wet etching are performed, to thus obtain aplurality of lower capacitor electrodes divided into unit memory cells.Then, a capacitor dielectric film 120 is formed to thus result in thestructure shown in FIG. 13. Thereon, a polysilicon film doped withimpurities is deposited and patterned, to thus form an upper (plate)capacitor electrode 125 on an upper part of the capacitor dielectricfilm 120 and thereby to complete a capacitor of a DRAM memory cell.

[0038] As mentioned above, in accordance with the present invention, andin a method of fabricating a storage capacitor in a semiconductor memorydevice and a storage capacitor structure, a capacitor electrode isadditionally formed even in the interior of a contact plug. Accordingly,a larger electrostatic capacity can be obtained in a restricted area.

[0039] Finally, although the present invention was described in detailabove in connection with the preferred embodiments thereof, the scope ofthe invention is not so limited. Rather, various changes andmodifications of the preferred embodiments, as will become apparent tothose of ordinary skill in the art, are seen to be within the truespirit and scope of the invention as defined by the appended claims.

We claim:
 1. A method of fabricating a storage capacitor of asemiconductor memory device, said method comprising: depositing a firstdielectric film and a second dielectric film on a substrate in an areawhere a memory cell transistor has been formed, and forming a definedfirst photoresist pattern on an upper part of the second dielectricfilm; anisotropically etching the second and first dielectric films byusing the first photoresist pattern as an etch mask, to form a firstcontact hole for exposing an activation region of the transistor;removing the first photoresist pattern, wet-etching the substrate withan etching solution having a difference in an etch ratio between thefirst and second dielectric films to form a second contact hole having anegative slope; depositing a conductive film to form within the secondcontact hole a contact plug of the storage capacitor having a voidtherein; performing an etchback to open an upper part of the void of thecontact plug; covering a structure produced by the preceding steps witha third dielectric film, and then forming a second photoresist patternfor defining a region where a storage capacitor electrode is to beformed; dry-etching the third dielectric film exposed through the secondphotoresist pattern; and removing the second photoresist pattern, andcovering a surface of the device with material to form the storagecapacitor electrode, to obtain the storage capacitor electrode having adouble cylindrical structure.
 2. The method of claim 1, wherein saidfirst dielectric film is an oxide film, and said second dielectric filmis a nitride film.
 3. The method of claim 1, wherein said etchingsolution is hydrofluoric acid (HF).
 4. The method of claim 1, whereinsaid conductive film that forms the contact plug is a doped polysiliconfilm.
 5. The method of claim 1, further comprising the steps of:covering the device an oxide film after obtaining the storage capacitorelectrode; and performing an etchback and wet etching, to separate thestorage capacitor electrode into unit memory cells.
 6. A storagecapacitor of a semiconductor memory device, comprising a structure of adouble cylinder which is extended by a constant depth from an upper partof a contact plug to a lower part thereof.
 7. A capacitor for asemiconductor device, comprising: a cylindrical contact plug disposedwithin a first dielectric film formed on a substrate, the cylindricalcontact plug having a first inner diameter and a first outer diameter; acylindrical lower electrode structure disposed on the cylindricalcontact plug, the cylindrical lower electrode structure having a secondinner diameter and a second outer diameter, where the second innerdiameter is greater than the first inner diameter and the second outerdiameter is greater than the first outer diameter; a second dielectricfilm covering an interior surface of the cylindrical contact plug andboth interior and exterior surfaces the cylindrical lower electrodestructure; and an upper electrode formed on the second dielectric film.8. The capacitor of claim 7 wherein the upper capacitor electrode isformed in part within an interior of the cylindrical contact plug. 9.The capacitor of claim 7, wherein the contact plug directly contacts thesubstrate at an area where an active region is formed.
 10. The capacitorof claim 7, wherein the capacitor dielectric film is atetra-ethyl-ortho-silicate (TEOS) film.
 11. The capacitor of claim 7,wherein the cylindrical lower electrode structure has hemisphericalgrains (HSGs) formed on a surface thereof.